Light polarizing materials are presently used to control the light transmission of certain windows. By constructing a window of two parallel panels, and covering each panel with a layer of linear polarizing material, light transmission control can be achieved by rotating one of the panels with respect to the other. When the polarization axes of the two panels are parallel to one another the transmission of the pair can be of the order of 40%; when one panel is rotated by 90 degrees so that the polarization axes of the panels are perpendicular to one another the transmission is reduced to the order of 1%. The variation between these two values is smooth as the rotation is accomplished, so that intermediate rotation amounts produce intermediate light transmissions. The practical problem with this arrangement is that nearly all windows used in homes and offices are rectangular in outline; rotating one panel with respect to another is awkward and requires a great deal of inefficiently utilized space for the corners of the windows.
U.S. Pat. No. 2,617,329 of John F. Dreyer describes an improvement where the polarizers in the panels are not uniformly oriented, but patterned in a particular way. This eliminates the need for rotation; the relative motion necessary to change the transmission of the window is translational. However, the pattern Dreyer requires causes manufacturing problems which are described below, and which result in local non-uniformities in transmission.
Here we describe a method of producing windows whose transmission can be varied smoothly and continuously over a wide range, remains uniform over the entire window aperture at all times, and does not require rotation. The polarization pattern proposed by Dreyer is modified significantly to permit manufacture without giving up any benefits.
The present invention provides a window made up of two parallel panels. Each panel carries linear light polarizing material. The orientation of the polarizing directions is not uniform over the panels; rather, it is at a particular angular value at each location on a panel. The variation of polarizing direction is smooth in some areas of the panel and discontinuous at other locations. The particular recipe for polarization angle as a function of location allows continuous variation of the light transmission of the pair of panels without requiring rotation of one panel with respect to the other. Instead a small translational movement is all that is required.
Since each panel carries polarizing material at every location in the window aperture, and since the angular orientation required does not vary smoothly over the entire window aperture, the polarizing materials are applied to more than one surface for each panel. These surfaces are then combined to form the complete polarized panel. Additional benefits are obtained by this method of construction: (A) improvements are found in durability of the polarizing materials because the act of combining elements to form a single panel permits sealing off the polarizing zones from ambient humidity; and, (B) evacuating the sealed regions permits the panels to reduce heat transmission just as in Thermopane windows.